Modified organopolysiloxanes have been prepared heretofore by polymerizing monomers containing aliphatic unsaturation in the presence of organopolysiloxanes containing terminal hydroxyl or hydrolyzable groups and free radical initiators as shown in U.S. Pat. Nos. 3,555,109 and 3,776,875 to Getson. Also U.S. Pat. No. 3,631,087 to Lewis describes a process for preparing modified organopolysiloxanes by gradually adding a mixture of monomers and free radical initiators to preheated organopolysiloxanes. U.S. Pat. No. 3,694,478 to Adams et al discloses a process for preparing modified organopolysiloxanes by the gradual addition of free radical initiators to a preheated mixture containing an organopolysiloxane and an organic monomer having aliphatic unsaturation. U.S. Pat. No. 4,032,499 to Kreuzer et al describes a process for preparing modified organopolysiloxanes by polymerizing monomers containing aliphatic unsaturation in the presence of organopolysiloxanes containing hydrolyzable or hydroxyl groups and free radical initiators and an inert liquid having a boiling point up to about 100.degree. C. at 760 mm Hg (abs.) in which the inert liquid is a nonsolvent for the organopolysiloxanes and the resultant reaction product at the polymerization temperature. It has been found that the modified organopolysiloxanes prepared above have a tendency to shrink during curing. This property is especially undesirable when the composition is used as a molding or potting composition.
Polyolefin filled vinylorganopolysiloxane compositions have been described in U.S. Pat. No. 4,014,851 to Bluestein, in which monomers having aliphatic unsaturation are polymerized in the presence of vinylorganopolysiloxanes and free radical initiators to form a two phase system, one being a continuous phase consisting of ungrafted vinylorganopolysiloxanes and the other phase being a discontinuous phase containing finely divided particles of ungrafted polymer.
Heretofore, it was thought that when organic monomers containing aliphatic unsaturation were polymerized in the presence of vinyl containing organopolysiloxanes, that the organic monomers or polymers would add to the vinyl groups and thus produce a composition which would be incapable of being cured by SiH addition. Surprisingly, applicant has found that monomers containing aliphatic unsaturation may be polymerized in the presence of vinyl containing organopolysiloxanes to form organopolysiloxanes having organic groups grafted thereto through a carbon-to-carbon linkage without destroying the ability of the vinyl containing organopolysiloxanes to react with SiH containing organosilicon compounds to form elastomeric solids. Moreover, applicant has found that the compositions obtained in accordance with this invention contain organopolysiloxanes having organic groups grafted to a silicon atom through a carbon-to-carbon linkage, whereas U.S. Pat. No. 4,014,851 teaches that the composition obtained from the process described therein is essentially free of grafted organopolysiloxanes.
Therefore, it is an object of this invention to provide an organopolysiloxane composition containing in situ generated particulate matter. Another object of this invention is to provide a method for preparing a modified organopolysiloxane composition in which at least one organopolysiloxane molecule has an organic group grafted thereto. Still another object of this invention is to prepare a modified organopolysiloxane composition by polymerizing vinyl monomers containing aliphatic unsaturation in the presence of vinyl containing organopolysiloxanes and free radical initiators. A further object of this invention is to provide curable compositions containing in situ generated particulate matter. A still further object of this invention is to provide elastomeric compositions having improved physical properties.